biology

SEMA7A

SEMA7A is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand SEMA7A rather than just read about it. In short: Semaphorin 7A, GPI membrane anchor (John Milton Hagen blood group) (SEMA7A) also known as CD108 (Cluster of Differentiation 108), is a human gene. SEMA7A is a membrane-bound semaphorin that associates with cell surfaces via a glycosylphosphatidylinositol (GPI) linkage.

Key takeaways

SEMA7A belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SEMA7A to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SEMA7A from memory before moving on to harder problems.

Reference excerpt

Semaphorin 7A, GPI membrane anchor (John Milton Hagen blood group) (SEMA7A) also known as CD108 (Cluster of Differentiation 108), is a human gene. SEMA7A is a membrane-bound semaphorin that associates with cell surfaces via a glycosylphosphatidylinositol (GPI) linkage. SEMA7A is also known as the John-Milton-Hagen (JMH) blood group antigen, an 80-kD glycoprotein expressed on activated lymphocytes and erythrocytes.[supplied by OMIM] SEMA7A is expressed in various adult tissues such as adipose, colon, esophagus, heart, brain, spleen, testis, lung, ovary, and uterus.

Development SEMA7A promotes axonal growth and is involved in mesoderm derived somite formation. Murine embryonic Sema7A expression is highest on day 7, which is indicative of its role on the differentiation of germ layer structure. Embryonic Sema7A expression is noticeable at all developmental stages as well as in the newborn and adult thymus, indicative of a development T-cell role. In wild type neurons, addition of Sema7A under in vitro conditions promotes elongation and branching in a dose dependent manner. Unlike the majority of semaphorins, SEMA7A enhances axonal growth and is imperative for proper embryonic axonal tract formation. Limited expression of SEMA7A is found in the hindbrain as opposed to an abundance of SEMA7A expression found in both the cranial and trunk neural crest cells, which indicates an involvement in migration and differentiation. Sema7A -/- mice show defects in olfactory tract development.

Tumorigenesis In normal breast tissue, mRNA expression of SEMA7A is low or not expressed, but activation to re-express SEMA7A occurs in these adult tissues to cause pleiotropic effects which increase tumorigenesis. Tumor cell growth, EMT, lung metastasis and angiogenesis have been linked to increased Sema7a expression in murine models. Increased SEMA7A expression correlates with poor prognosis in breast cancer patients. Tumors increase SEMA7A expression in an involuting environment, but knockout of SEMA7a in mouse models undergoing involution decreases lymphangiogenesis.

Genetics This protein is known to have eight variants in the extracellular region: seven lie within the Sema domain and one within the PSI domain.

Molecular biology This protein forms dimers.

Notes This protein acts as a receptor for the malaria parasite Plasmodium falciparum.

Illustrations

Worked examples

Example 1 — a first encounter with SEMA7A

Start with the simplest possible case. Write down what SEMA7A claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SEMA7A before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SEMA7A ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SEMA7A

In research: SEMA7A appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SEMA7A in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SEMA7A is common in secondary-school and first-year university syllabi. It links to neighbouring topics Blood antigen systems, Clusters of differentiation, Genes on human chromosome 15, so understanding it makes those chapters shorter.
In everyday life: Look for SEMA7A outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study SEMA7A in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SEMA7A means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SEMA7A out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SEMA7A in simple terms?

Why does SEMA7A matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SEMA7A?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SEMA7A.